I postulate that Facebook causes damage to social relationships. Damage that is direct, elusive and difficult to repair. This may seem counterintuitive, considering Facebook is all about "The Social", "Networking", "Keeping in touch" and all that. However, I will attempt to show this is part of the problem. This is applicable to a high degree to other social networking services as well, but Facebook is the one I have had the most contact with. Feel free to mentally substitute StudiVZ, myspace, or any other similar service.
First, let me state my biases. I am not a Facebook user. I do not intend to be. I also do not use any other service that is primarily a social network. I spend most of my life these days in a social psychology research group. Most of my coworkers are on a Facebook equivalent. As far as I am aware, all of my former classmates are on Facebook. Most of the people I meet in various non-work settings are on Facebook. A majority of my Internet-only contacts are Facebook users. I have had the opportunity to observe the use (by others) of this and several other similar services in a lot of detail over the past months. I get asked why I am not a member on average once every two to three weeks. This writeup is a summary of what I have thought about the subject and what I have been telling people.
Facebook, and to a degree all other social networking services have several effects that are detrimental to social relationships. The ones I am aware of are, in no particular order:
I will examine each of these in turn.
Trivializing friendship and personal relationships
Facebook uses suggestive terms to emphasize the "social" aspect of itself. This may appear harmless but it has an effect on how the system and its usage are perceived by its users. In my opinion the most significant of these is the way Facebook uses "friend" to mean "contact". These two are most definitely not interchangeable terms. Adding someone as a "friend" is the minimal form of direct relationship that can be established within the network. In my observation, this often leads to people who would be better described as "acquaintances" being entered into the system as "friends". This dilutes the concept of friendship and introduces an artificial equality amongst different classes of relationship, where there is no clear separation between people who have known each other for years and someone who first established contact hours ago.
Personal communication has a long tradition. Practical reasons have restricted personal communication to small groups of people, and most explicit personal communication happens on an inter-individual level. This means that a person communicating something to another has to explicitly make the effort of transmitting the message, and to consider the recipient of the message and their likely reaction. This adaptation of the content to the recipient makes the message personal. Naturally this involves a specific effort from the sender for each recipient, limiting the effective size of their social circle to the point that they have to choose whom they communicate with more intimately and who are only worth superficial "keeping in touch". Facebook reverses this relation, shifting the effort from the sender to the recipient. The action of explicit communication with a specific person is transformed into an "update" of one's personal data. It is then up to the recipients to follow a set of feeds and determine which bits of the content are relevant to them. The sender is now broadcasting a message to a large and heterogenous group of "friends" (who, as discussed above, may be at any level of closeness) and therefore to nobody in particular. The message loses its personality by not being individually addressed. On the side of the recipient, there is no indication that the sender has any commitment to the social connection between the two, as there is with explicit personal communication. Links between people become implicit, and the overall depth of the content is necessarily reduced as the set of "friends" includes some people who cannot be trusted as much as others. The closest friends suffer the most from this arrangement. The most common update to profiles I've observed seems to take the form of a contact publishing their result from one of the myriad of quizzes floating around on the site.
Creating the illusion of contact
In itself, being able to publish personal information to your entire contact list is not harmful. However, whether due to heavy marketing of the service as a primary method of keeping in touch or another reason I am not aware of, many users seem to feel that since they are updating their profiles with everything that happens in their lives, they no longer need to tell their friends these things. The result of this is that the communication of various important things in users' lives to their closest friends is reduced to the watered-down, contact list-safe version, necessarily reducing detail and intimacy. At the same time, the recipients of this information can passively follow the feed of new updates and feel they are aware of and connected to the other person, even though the depth of interaction never goes beyond the most superficial. Multiple users of the service that I interviewed reported that they have reduced the use of personal emails, instant messages and phone calls to communicate directly with their friends since they actively started using Facebook. For several, Facebook had become the primary, and for a few the exclusive communication tool for contact with friends at a distant location. People who live close to their friends do not seem to be affected as much, suggesting that they still prefer face to face communication. I would be glad to receive more data on this from others.
A central element of Facebook are communities and groups. These tend to build around real-life communities whose members are Facebook users. In many cases it becomes a major communication channel for that community. This is due to the fact that unlike group-specific public forums, a Facebook group does not need to be explicitly visited and checked for new content. This is done implicitly since the Facebook users are already visiting the Facebook site to view updates from their contacts. Having their communities represented on Facebook gives them one less place to look to find information. However, while this is convenient for Facebook users, these communities are available to users only. This means that community members that are not also Facebook users will be left out of the loop for at least some part of the communication relevant to the community. Due to the added convenience for existing users, they are strongly motivated to induce non-users to join the service. When a majority of the community is on Facebook, it is possible that even most of the critical information related to it will never leave the site.
When users use the service as members of various communities, they may be reluctant to share too much personal information with other group members. If the service is also their primary communication medium for personal relationships, this reluctance acts to further reduce the depth of communication towards close friends. Publishing large amounts of very intimate personal information online creates fears that current and/or future employers will access and interpret this information. Publishing personal information carries much more responsibility than communicating it privately. In the latter case there is a specific trust relation that is applied to the content of the communication, in the former it needs to be reduced to the publishable subset of this information. As stated above, in many cases the publishable information is all that is transmitted, though close friends are often more interested in the unpublishable bits.
Promoting mass invasion of privacy
As a counterpoint to the above, peer pressure from contacts who use Facebook as a primary communication channel is a push to publish as much personal information as possible. The branding of the site as "social" in every possible way suggests that users who do not publish their own information are not being "social"., which carries a very heavy negative stigma in today's society. Since people want to appear more social in most situations, they will publish large amounts of information to their entire contact list. How the service operators use this information is an issue in itself, but even assuming they respect the privacy of users (as Facebook has been repeatedly shown not to) the publication of exceedingly private information to the entire contact list is harmful in itself as the user feels they are required to give up privacy to "stay in touch".
Consuming large amounts of time
Finally, Facebook and similar sites consume a very large amount of time. I have personally observed people using the site for multiple hours a day, most days of the week. This is not universal, but is sufficiently prevalent to be a possible problem, particularly as the time spent using Facebook is often interpreted by users as "time spent socializing", which is problematic in itself as it is possibly time taken from actual interpersonal contact. Again, this is not a universal problem, and mostly stems from the strong "social" branding of the service.
Given these points, I want to state my personal viewpoint clearly. I have made a strong personal decision to not use these services for "keeping in touch" with friends, at least not friends I care to keep. I prefer infrequent but personal contact to a constant feed of largely zero-content information. Yet I get constant requests to join the site, and I am left out of a lot of loops because communities I attempt to participate in communicate primarily using Facebook. I have found it is possible to manage this way and obtain information by asking people directly, but it requires a lot of effort from my side. Keeping in touch personally does require effort, and it is effort I am willing to make for my friends. However, I feel my social life as a non-member has been hurt somewhat by the existence and widespread use of this service. In the case of many of my friends who now live away from me, since they have started using the service I receive less personal communications that are not answers to ones of my own. I find I need to initiate communication most of the time. I find people are confused and surprised by receiving a personal email. I do not believe this is a good thing. I therefore suggest that using Facebook is dangerous and destructive to personal relationships. Don't "friend" your friends if you want to keep them.
Six hours since I wrote this and I am already overwhelmed with feedback. Multiple noders tell me they use the site in a different way from what I've described. Some state that they restrict usage only to close friends, others go in the other direction and use it only for acquaintances. However, I still maintain that the attitude the site suggests is to "friend" many people, and this is how I see people around me use it. I'd love to hear more from noders who use it in different ways.